The present invention relates to a write-once optical information recording medium in which a high-quality information signal can be recorded and reproduced by emitting a high energy beam such as a laser beam to a thin film formed on its substrate. The present invention further relates to a manufacturing method, a recording and reproduction method, and a recording/reproduction device for the same.
A technique to record and reproduce an information signal by forming a thin film on a transparent substrate and emitting a laser beam focused as a minute spot on this thin film is well known. As an example of such a write-once recording medium used for recording and reproduction, JP50(1975)-46317A discloses a recording medium that is provided on its substrate with a material thin film mainly composed of TeOx (0 less than x less than 2), which is a mixture of Te and TeO2. With the use of such a recording medium, a considerable reflectance change can be obtained by emitting an optical beam for reproduction.
This recording thin film mainly composed of TeOx can record an information signal in an amorphous state after deposition without performing an initialization process such as a laser annealing, and by modulating an intensity of a laser beam and emitting the laser beam to form crystal marks. This is an irreversible process in which a correction by overwriting or a deletion cannot be performed, so that this recording thin film has important characteristics as a write-once recording medium as well. Furthermore, the recording thin film mainly composed of TeOx has excellent environmental stability such as moisture resistance and does not require a dielectric protective layer or the like. Therefore, the recording medium usually can be used as a single-layer thin film, which is also preferable with respect to the production cost.
However, TeOx requires some time until recorded signals become saturated, that is, until a crystallization process within a recording thin film proceeds sufficiently by irradiation of a laser beam. This aspect is unsuitable as a recording medium from which a rapid response is required, for example, in case of a computer data file in which data are recorded in a disc and the data are verified after one rotation. To compensate for this disadvantage, a recording medium is disclosed in which Pd or Au is added to TeOx as a third element (JP60(1985)-203490A, JP61(1986)-68296A, JP62(1987)-88152A). Pd or Au is believed to promote the crystal growth of Te inside a TeOx thin film during irradiation of a laser beam. Thereby, crystal grains of Te and Texe2x80x94Pd alloy or Texe2x80x94Au alloy are produced at a high speed. As a result thereof, a high-speed crystallization recording becomes possible, and the rapid response mentioned above can be obtained. In addition, due to its high oxidation resistance, Pd or Au does not impair the moisture resistance of a TeOx thin film.
Furthermore, as basic means for increasing the amount of information to be handled by one piece of medium, there is a method for improving the areal recording density by reducing a spot diameter of a laser beam, which is achieved either by shortening a wavelength of the laser beam or by increasing a numerical aperture of an objective lens that focuses this laser beam. In addition, for the purpose of improving the recording density in the circumferential direction, a mark edge recording in which the length of a recording mark serves as information is invented and introduced. Also, for the purpose of improving the recording density in the radial direction, a land and groove recording in which grooves for guidance of a laser beam and portions between the grooves (lands) are both used for recording is invented and introduced. To increase the amount of information to be handled by one piece of medium, there are proposed a multilayer structure medium including a plurality of layers laminated for recording and reproduction of information, a method for recording and reproduction of the same (JP9(1997)-212917A, JP10(1998)-505188A, JP2000-36130B etc.), and layer recognition means as well as layer switching means for selecting one layer from such a plurality of information layers to perform recording and reproduction (JP10(1998)-505188A).
To support such high density recording, a recording medium with improvements of the composition and the film thickness of a recording material, which is made of TeOx to which Pd or Au is added as a third element, is proposed (JP9(1997)-326135A, WO 98/09823A).
However, along with a capacity increase of information in recent years, there is a demand for a further improvement of recording density, and thus, an optical system with a shorter wavelength and a higher numerical aperture (NA), particularly a recording medium applicable to high-density recording using a violet laser beam, needs to be developed.
Even if the wavelength of a laser beam used for recording and reproduction is changed, the thermal characteristics of a recording material are basically the same. However, the optical characteristics, particularly the optical constant may change greatly due to the material. Particularly in a violet wavelength region as compared to a red wavelength region, a recording material based on TeOx has a smaller reflectance change, and a signal amplitude to be obtained as well as a C/N ratio also tend to become small.
It is an object of the present invention to provide a write-once optical information recording medium, from which excellent recording reproduction characteristics with a high C/N ratio can be obtained even for recording and reproduction of high density information using a violet laser beam. Another object is to provide a manufacturing method, a recording and reproduction method, and a recording reproduction device for the same.
To achieve the above objects, an optical information recording medium of the present invention comprises a transparent substrate on which an information layer is disposed, the information layer comprising a recording layer and a dielectric layer, and the recording layer containing Te, O and M (wherein M is one or more elements selected from Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, Au and Bi), wherein a content ratio of O-atom in the recording layer ranges from 25 atomic percent to 60 atomic percent, and a content ratio of M-atom therein ranges from 1 atomic percent to 35 atomic percent, and a refractive index n of the dielectric layer is not less than 1.5.
Next, a first manufacturing method for an optical information recording medium of the present invention is a method for manufacturing an optical information recording medium comprising a transparent substrate on which an information layer is disposed, the information layer comprising a recording layer and a dielectric layer. The method comprises
forming a recording layer containing Te, O and M (wherein M is one or more elements selected from Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, Au and Bi) and a dielectric layer having a refractive index n of not less than 1.5 by a gas phase thin film deposition, wherein a content ratio of O-atom in the recording layer ranges from 25 atomic percent to 60 atomic percent, a content ratio of M-atom therein ranges from 1 atomic percent to 35 atomic percent, and
conducting an annealing by maintaining a temperature of 60xc2x0 C. or higher for at least 5 minutes.
Next, a second manufacturing method for an optical information recording medium of the present invention is a method for manufacturing an optical information recording medium comprising a transparent substrate, an information layer disposed thereon, and a protective layer disposed further thereon. The method comprises
forming the protective layer first, and
forming a recording layer containing Te, O and M (wherein M is one or more elements selected from Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, Au and Bi) and a dielectric layer having a refractive index n of not less than 1.5 by a gas phase thin film deposition, wherein a content ratio of O-atom in said recording layer ranges from 25 atomic percent to 60 atomic percent, and a content ratio of M-atom therein ranges from 1 atomic percent to 35 atomic percent, and, before or after said transparent substrate is attached to the information layer, conducting an annealing by maintaining a temperature of 60xc2x0 C. or higher for at least 5 minutes.
Next, a recording and reproduction method for an optical information recording medium of the present invention is to record or reproduce an information signal in an optical information recording medium, which comprises a transparent substrate on which an information layer is disposed, the information layer comprising a recording layer and a dielectric layer, the recording layer containing Te, O and M (wherein M is one or more elements selected from Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, Au and Bi), wherein a content ratio of O-atom in the recording layer ranges from 25 atomic percent to 60 atomic percent, and a content ratio of M-atom therein ranges from 1 atomic percent to 35 atomic percent, and a refractive index n of the dielectric layer is not less than 1.5. The method comprises emitting an optical beam at a wavelength of not more than 500 nm to the optical information recording medium from a side of the transparent substrate.
Next, a recording and reproduction device for an optical information recording medium of the present invention comprises optical beam generation means for emitting an optical beam at a wavelength of not more than 500 nm for recording and reproduction of an information signal, and optical beam modulation means for, when forming a mark, modulating the optical beam with a pulse waveform including pulse trains with different pulse numbers depending on a length of the mark.
According to the present invention, it is possible to provide a write-once optical information recording medium, from which excellent recording reproduction characteristics with a high C/N ratio can be obtained even for recording and reproduction of high density information using a violet laser beam, a manufacturing method, a recording and reproduction method and a recording reproduction device for the same.